Power system analysis results are based on a model of the system. The model is often assumed known, yet it may contain errors. Model errors can impact the accuracy of the results. This paper utilizes historical data over time to extract the transmission line model parameters. The focus is on application of line parameter estimation techniques for real data from a North American utility. The approach in this paper focuses on the challenges of dealing with uncertainty and errors encountered in the real-world data. Future applications are also discussed.